1. Field of the Invention
This invention is in the field of heat treatment of fine grained particles such as in the calcination of particles in the manufacture of cement and is directed to a system employing serially connected cyclone separators as the heat exchange means, and supplemental combustion means positioned in the path of travel of the particles through the heat exchange means.
2. Description of the Prior Art
The treatment of fine grained material in a calcination furnace, utilizing exhaust gases from the furnace for the preheating and deacidification of pulverized raw material used in the manufacture of cement is a highly developed art. Typically, such installations include several cyclone separators connected in series and joined by means of conduits. The great majority of such installations are characterized by cyclone separators through which the treatment gas flowed, the cyclone separators being arranged with relatively large spacing in order to make possible the flow through of the fine grained material by the force of gravity. It is also thought necessary to use such substantial spacings to obtain sufficiently long burn-out stretches particularly in the conduits between the calcination furnace and the hottest step of the heat exchanger. The result of this type of construction manifests itself in a relatively large vertical height as evidenced, for example, by German Patent No. 1,282,232.
In U.S. Pat. No. 3,235,239 there is described a multiple cyclone heat exchanger for a cement manufacturing installation in which the hot treatment gases consecutively flow through cyclone separators from a rotary kiln and from a combustion chamber with additional firing. These cyclone separators are arranged horizontally adjacent one another. This type of arrangement necessarily results in very great spacings between the elements of the heat exchanger. The long gas and material conveying conduits required provide additional investment costs. Furthermore, the long gas conduits lead to high pressure losses in this system, so that the economy of the system is greatly impaired. Moreover, technical difficulties have been experienced in such systems, resulting from high losses in pressure in the long gas conduits, and caking deposits of materials on the conduit walls.